So far, the traffic generated in mobile networks such as e.g. GERAN (GSM (Global System for Mobile communications) EDGE (Enhanced Data rates for GSM Evolution) Radio Access Network) and UTRAN (UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network) has mostly been dominated by services that require human interaction, such as e.g. regular speech calls, web surfing, sending MMS, doing video-chats etc, and the same traffic pattern is also anticipated for E-UTRAN (Evolved-UTRAN). As a natural consequence, these mobile networks are designed and optimized primarily for these “Human Type Communication” (HTC) services.
There is, however, an increasing market segment for Machine Type Communication (MTC) services, which do not necessarily need human interaction. MTC services include a very diverse flora of applications, ranging from e.g. vehicle applications (such as automatic emergency calls, remote diagnostics and telematics, vehicle tracking etc.) to gas and power meter readings, and also network surveillance and cameras, to just give a few examples. The demands that MTC services put on the mobile network, e.g. in terms of the number of communication devices to be served in the network, will without any doubt significantly differ from what is provided by today's HTC-optimized mobile networks. Thus, in order for mobile networks such as GERAN and UTRAN to be competitive for these mass market MTC applications and devices, it is important to optimize the support of such networks for MTC communication.
One of the critical issues in e.g. GERAN is how to distinguish and properly address a vast number of devices for the case of simultaneous data transfer on shared radio resources, since the available addressing spaces may not be sufficient. One of the identifiers that may be a bottleneck in this respect is the so-called Temporary Flow Identity (TFI) which is assigned by the GERAN network to each Temporary Block Flow (TBF) for the purpose of e.g. identifying a particular TBF and the transmitted Radio Link Control/Medium Access Control (RLC/MAC) blocks associated with that TBF.
In GSM data is sent and received in a time division manner; one Time Division Multiple Access (TDMA) frame is divided into eight timeslots. These timeslots can be used for either voice, data or signaling. To transfer data, a Temporary Block Flow (TBF) needs to be set up on one or more timeslots, and it is identified by a Temporary Flow Identity (TFI). Each TBF is assigned a TFI value by the mobile network. The addressing of the mobile station in GPRS/EDGE transfer mode is handled by the TA. The uplink and downlink TFI value is unique per TBF and assigned Packet Data Channel (PDCH, a timeslot reserved for the packet switched domain). This limits the number of concurrent TBFs and thus the number of devices that may share the same radio resources.
In the header of an RLC/MAC block for data transfer, the TFI identifies the TBF to which the RLC data block belongs. For the downlink and uplink TFI, the TFI itself is a 5-bit field encoded as a binary number in the range 0 to 31, which is typically provided to the mobile station (MS) by the GERAN network upon assignment of the TBF. This means that, for example, every time an MS receives a downlink data or control block, it will use the included TFI field to determine if this block belongs to any (there can be more than one) of the TBFs associated with that very MS. If so, the block is obviously intended for this MS, whereupon the corresponding payload is decoded and delivered to upper layers, and is discarded otherwise. In the uplink direction the behavior is similar, i.e. the mobile network uses the TFI value to identify blocks that belong to the same TBF.
To multiplex mobile stations on the uplink an Uplink State Flag (USF) is available for each PDCH. The USF field is sent in all downlink RLC/MAC blocks. When a mobile station reads its own USF value on a PDCH it is assigned with, it knows that it is allowed to transmit on that timeslot in the next radio block period. The USF field is 3 bits in length and 8 different USF values can be assigned. One USF value normally needs to be reserved for uplink blocks scheduled by other means than USF, leaving 7 USF values that can be used for scheduling of UL TBFs.
The numbers of possible TFI values are limited by the available 5 bits, which thus allows for 32 individual values. This may appear sufficient, and has until now provided no significant limitation. There are however a number of indicators that the TFI addressing space may be a limiter in the future.
If a TBF is assigned to be used on more than one PDCH (which is most often the case) the number of usable TFIs per PDCH drastically decreases. Assume e.g. that all TBFs are used on all 8 PDCHs. This means that the average number of TFIs per PDCH will be 32/8=4, as compared to the 32 TFIs per PDCH that would be the case otherwise. In most situations it is desirable to spread a TBF over as many PDCHs as possible in order to improve the statistical multiplexing gain and flexibility, but this has the drawback of reducing the potential number of TBFs that can be supported on any given set of PDCHs.
With recent additions to the 3GPP (3rd Generation Partnership Project) standards which allow the use of multiple TBFs associated with one and the same MS by means of Multiple TBF procedures and/or Enhanced Multiplexing of a Single TBF (EMST), the number of TBFs associated with any given MS will no longer be limited to one per direction. One particular MS could now e.g. in the downlink have one TBF for a web-surfing session, another for an ongoing voice call and finally a third for a messaging service such as MSN. The benefit on splitting these particular services over different TBFs is of course that they all have different service requirements, but an obvious drawback is that more TFIs are needed.
The amount of Packet Switched (PS) traffic in a typical GERAN network is continuously and rapidly increasing already today, with the usage of classical HTC services as described above. Bearing in mind the anticipated vast increase in the number of HTC+MTC devices in the near future, it is more than likely that the PS traffic volume in GERAN, and implicitly the number of TBFs per transmitter, will increase manifold. It is not at all an unlikely situation that for these kinds of services, it would be beneficial to multiplex perhaps dozens or more users of the same uplink PDCH.
There is therefore a need for a solution for allocating radio resources for communication devices in a wireless communication network, such as GERAN, that will increase the number of communication devices that can be used simultaneously in the communication network.